1. Field of the Invention
The present invention relates to asphalt roofing shingles. More specifically, the present invention relates to self-annealing asphalt shingles containing one or more chloride salts. The shingles disclosed herein remain flexible and pliant at sub-freezing temperatures, thereby preventing snow and ice from creeping underneath the shingles.
2. Description of the Prior Art
In upper latitudes and elevations, where the ambient temperature falls below freezing, and especially where there is a significant amount of snow fall, a chronic problem encountered by homeowners is water which gains unwanted entry into a dwelling. Typically, this nuisance occurs when the ambient temperature quickly cycles between warmer temperatures, and sub-freezing temperatures, or when there is a significant amount of snow fall followed by a rapid temperature rise.
What often occurs in these instances is that the roofing shingles which protect and waterproof the roof of a dwelling become frozen and lose their resiliency at sub-freezing temperatures. This lack of resiliency allows ice (which occupies a greater volume per unit mass than liquid water, and which has formed at the edge of the shingle) to "creep" underneath the stiffened shingle. This creep effect is exacerbated when the ambient temperature goes through a rapid thaw-freeze cycle because the ice originally trapped underneath a row of shingles does not completely thaw. When the temperature again falls below freezing, the ice trapped below the shingle is forced even further underneath the stiffened shingle by ice being newly formed at the exterior edge of the shingle.
Once the ice underneath the shingle is forced over the interior edge of the shingle, it comes in contact with the roof sheathing. Once in contact with the roof sheathing, heat from inside the dwelling is normally great enough to melt the ice, which then drips through the sheathing. The damage caused by such leakage can range from a minor nuisance to widespread destruction of the roof sheathing and interior plaster structures such as ceilings and walls.
Clearly, then, there is a need for an improved shingle which has a low-temperature stiffening point, and which remains flexible and pliant at sub-freezing temperatures. Such a shingle should also be of simple construction, and manufactured from readily available and inexpensive commodity materials.
Several different types and styles of shingles and other construction materials are described in the patent literature. Of particular note to the present disclosure is U.S. Pat. No. 3,830,687, issued Aug. 30, 1974, to Re et al. This reference describes a flame retardant roofing material designed to simulate wooden shake shingles. The roofing material includes a core of a gypsum material enclosed within a fiberglass shell containing fire-resistant materials such as asbestos. The core-shell construction of this simulated shake shingle is far more complex, and more costly to construct than the presently claimed shingle.
U.S. Pat. No. 4,047,962, issued Sep. 13, 1977, to Copeland, describes a moldable construction composition which can be wet mixed and utilized in pouring building walls, floors and the like. A preferred embodiment of the composition includes gypsum, vermiculite, portland cement, wood fibers, calcium chloride, sisal or polypropylene fiber, and water. The wet mixture is then allowed to cure to form a shrink-resistant construction material.
Another wet-mixed cement composition is described in U.S. Pat. No. 4,482,379, issued Nov. 13, 1984, to Dibrell. Dibrell describes a pumpable slurry containing a hydraulic cement, gypsum, calcium chloride, and a setting time retarding agent. The cement may also include an additive blend containing sodium metasilicate, lime, and hydroxyethyl cellulose. When cured, the composition displays good compressive strength at low temperatures.
U.S. Pat. No. 5,194,091, issued Mar. 16, 1993, to Laney, discloses a geopolymer-modified gypsum-based construction material. Here, a geopolymer adhesive is admixed with a conventional gypsum wallboard slurry. This produces an interpenetrating network which cures by the loss of process water. The resulting refractory solid is fire and water-resistant. The geopolymer adhesive component includes soluble and insoluble silicates, buffers, salts in aqueous suspension, and chemical setting agents.
U.S. Pat. No. 5,287,669, issued Feb. 22, 1994, to Hannah et al., describes a roofing shingle having very specific physical dimensions. Specifically, the shingle has an exposure height of 8 inches relative to an overall height of 18 inches. The shingles have 3 or 4 tabs, and a ratio of exposure height to tab width of either 0.667 or 0.889. These dimensions allow more shingles to be manufactured from a sheet of shingle material. Additionally, due to the ratio of the tabs, exposure height, and overall height of the shingle, a roof can be installed using fewer nails.
The remaining references cited on the form PTO-1449 submitted with the application are seen as being cumulative to the above-described references.
None of the above references, taken alone, or in any combination, is seen as describing the presently claimed shingle composition.